The biochemical processes underlying the neuroendocrine occurrence and function of neurophysins (NP's) and associated neuropeptide hormones oxytocin and vasopressin have been studied. The NP's and neuropeptides are dominant polypeptides of the hypothalamo-neurohypophyseal system ("classical" site of occurrence). Their intraneuronal biosynthesis, translocation, and structural transitions from precursors to mature, interacting polypeptides comprise major elements of neurosecretory functions. NP and neuropeptide hormone-related polypeptides also have been detected, in less abundance, in putative neuromodulator-neurotransmitter pathways within the central nervous system as well as in several peripheral (e.g. endocrine) sites ("non-classical" sites of occurrence). In one aspect of the present work, a study has been continued to define the processing reactions, including enzymes involved, which produce neuropeptide hormones and associated NP's from common biosynthetic precursors. A synthetic dodecapeptide containing the sequence of oxytocin with a C-terminal tripeptide extension (that acts in the whole precursor as a spacer between hormone and NP) has allowed detection and partial isolation and characterization of the carboxypeptidase B-like protease from neurosecretory granules. Also, a theory has been developed that precursor processing and packaging are regulated by self-association of precursor molecules which likely occurs upon biosynthesis and packaging of precursor into neurosecretory granules. A basic observation to support this thesis has been made by quantitative affinity chromatographic analysis of radiolabelled rat NP/hormone precursors on immobilized bovine NP affinity matrix. Separately, two studies have been initiated of the biochemical events occurring in "non-classical" sites of the NP/hormone neuroendocrine system. One involves characterization of the ovarian occurrence of neuropeptides and NP's. Included is an effort to identify not only the structural nature of hormone - and NP - immunoreactive molecules in the ovarian locus but also the anatomical origin of these polypeptides and ultimately their function in this endocrine site. A second study involves efforts to identify receptors for the neuropeptides by radioreceptor assay of various membrane fractions isolated from neuronal and related sites.